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Evil Reostat!

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Tomsawyer

Member
Joined
Jan 5, 2001
2 120mm fans have overwhelmed my 300ohm reostat. Drat I knew I should have gone 150ohm. Now its either full speed or no fans and for water cooling thats not good. Sigh good thing they are only 1 buck down at Skycraft.
 

jonk

New Member
Joined
Feb 15, 2001
I recently hooked up a YS-Tech 120mm 3wire fan with the power connected thru a rheostat to the PS, and the tach wire to the mobo header (CUSL-2). When the fan is up full, the BIOS (and MBM5) don't report the fan's rpm (BIOS says n/a, and MBM5 says 0 rpm). When I turn the fan speed down, the fan speed starts to register, but is incorrect. (the fan is rated 2800 rpm, but starts to show in both BIOS & MBM5 at about 5000 with the rheostat turned down about halfway).
Any ideas??
 

Tim-

Senior Member
Joined
Dec 18, 2000
Location
North Carolina
Changing to a 150 ohm rheostat may not make any difference and will probably make things worse- you want to increase the power rating, not change the resistance. Get a 5 watt part instead of a 1 or 2 watt or else it will likely happen again.
 

DamnFast

Member
Joined
Feb 1, 2001
I got my 25 Ohm Rhestat from Radioshack for 2.99 each. They are connected to Panaflo 120mm fan and works just fine. This panaflo fans are rated at 5~6watt and the 25 Ohm rheostat from radiashack is rated about the same.5.5 or 5.6 watt total. So as long as you have proper watt power, you'll be fine.
 

Colin

Arctic Silver Senior
Joined
Dec 19, 2000
Go to the Shack an buy a LM317 voltage regulator. The circuit is on the back of the package. Put a 1uf elctrolytic cap and a .1uf ceramic cap on the output and a .1uf and .01uf ceramic caps on the input. This is the professional way of dealing with fan speed. Rheostats suck.
 

DamnFast

Member
Joined
Feb 1, 2001
Colin (Feb 20, 2001 02:27 a.m.):
Go to the Shack an buy a LM317 voltage regulator. The circuit is on the back of the package. Put a 1uf elctrolytic cap and a .1uf ceramic cap on the output and a .1uf and .01uf ceramic caps on the input. This is the professional way of dealing with fan speed. Rheostats suck.

Yea...but what about people who don't really know the "professional" way you're talking about? I believe that if the rheostat works just as fine as the "professional" voltage meter you're talking about, why go through all that trouble? It saves money as well.
 
OP
Tomsawyer

Tomsawyer

Member
Joined
Jan 5, 2001
Rear fan blowing on cooling coils is now pluged directly into the power supply so it can run full speed. The new rheostat is controlling the front just fine. Still holding at 26C idle, and 34C max load :)
 

Colin

Arctic Silver Senior
Joined
Dec 19, 2000
Tom,

Rheostats are a dirty way of dealing with voltage. In the extreme imagine a block of dry ice as a CPU cooler. They have mechanical parts that will eventually fail compared with a reliable electronic voltage regulator. The overall cost is very close. It’s the human time and effort that makes the difference. When I get back from my vacation next week, I would be happy to help you with building a multiple LM317 circuit.

Colin
 

Mr_Goat

Member
Joined
Jan 15, 2001
Location
Poland
Hey Colin, I think you confused a Rheostat with a Potentiometer, Rheo's do current and have two terminals and Pots have three and do voltage...you can wire a Pot to act as a Rheo...
 

Colin

Arctic Silver Senior
Joined
Dec 19, 2000
Pots have three terminals too. From the back, center is common, right gives increasing resistance with clockwise rotation, left gives increasing resistance with counterclockwise rotation. Rheostats are just wire wound pots that can handle more current. Solid state devices are still a better choice for voltage regulation.
 

Mr_Goat

Member
Joined
Jan 15, 2001
Location
Poland
Yeah, I agree that solid state is much better, but whats the MTBF for a pot/rheo? Or are they rated in a different way (duty cycles?)? Definately, last longer then dry ice ;-)
 
OP
Tomsawyer

Tomsawyer

Member
Joined
Jan 5, 2001
Collin,

Thanks for the aid bro, but I am using the reostats as I have a box of them now for free. I know voltage systems are better (dual major in computer science and pyschology) but for now I just turn the knob :)